Molding process



May 14, 1940. H. F. HAGEMEYER MOLDING PROCESS Filed April 23, 1938 2Sheets-Sheet 1 W M M:

INVENTOR HENRYFH/IGEMYER W ATTOR NEY May 1940.

H. F. HAGEMEYER MOLDING moor-ass Filed April 23, 1938 2 Sheets-Sheet 2 INVENTO R HENRY E'Hfle'amm ATTORNEY Patented May 14, 1940 PATENT OFFICEMOLDING PROCESS Henry F. Hagemeyer, Chicago, Ill., assignor toCastiilisgs Patent Corporation, a corporation of Application April 23,1938, Serial No. 203,872

9 Claim.

This invention pertains to a process for producing molds and inparticular to the production of molds having gypsum as a basis of themold material. This application is a continuation in part of myapplications Serial No. 87,922, filed June 29, 1936, for Moldingapparatus, continuation in part thereof filed May 5, 1938, as Serial No.206,152, for Molding methods and apparatus) and Serial No. 91,897, filedJuly 22, 1936, for Drying apparatus, (see divisional application SerialNo. 206,151, filed May 5, 1938, for Mold drying methods and apparatus)and is a companion to the application resulting in my Patent No.2,101,677, issued December I, 1937, for Apparatus for producing moldsand reissued as Re.

21,046 on April 11, 1989.

Molds having gypsum as a principal ingredient have long been proposedfor use in a commercial general casting process, but prior to thedevelopment of my method such molds have been very expensive to make andhave been difficult to pour satisfactorily. The expense has arisenlargely because of the great length of time and the care required to drythe molds, despite which the percentage of molds broken or cracked toobadly to use was high, and the difiiculty of pouring largely arosebecause of insufilcient porosity of the mold to convey away the airtrapped in the mold cavity and the pouring gases. It has been desiredtopour such molds without the provision of a venting passage in additionto the sprue and gate.

The history of the art is replete with suggestions for increasing theporosity, of the mold material, but invariably pouring the metal under-pressure has been necessary to fill the mold cavity. With suflicientporosity of the mold the metal will flow into even the tiniest detailand branch of the mold cavity without pressure, the air and gasesexuding through the walls of the cavity ahead of the inflowing metal.

In an attempt to obtain suflicient porosity of the mold material toallow this action, various skilled artisans have suggested mixing withthe gypsum a fibrous or a granular material, among which appearasbestos, other rock of the homblende family, coal ashes, a combinationof potters clay and asbestos, powdered carborundum, a combination ofasbestos fiber and brick dust,

U and kieselguhr or cellite. None of these substances has proved to becapable of obtaining the porosity required.

A sand mold is rather porous, but it has other disadvantages, namely,the moisture therein causes a large amount of pouring gas especiallywhen casting brass. The sand mold chills the hot metal comparativelyquickly and prevents its flow into small crevices. The surface of a sandmold, and hence the resultant casting is granular instead of smooth.

In my process I am able to obtain great porosity in the mold, not bymixing the gypsum with a granular material, but by mixing in with thedry material a great excess of liquid, preferably water, which, afterthe mold is set, is evaporated out of it, to leave voids or cavities inthe mold. Despite such great excess of liquid I am able to dry outthemold ready for pouring in an hour or two by the application to allsurfaces of each mold section of direct radiant heat. Such exposure isobtained by removing the mold sections from the flask and match plate assoon as the gypsum is somewhat set, the setting being expedited andcontrolled to obtain a minimum meniscus by employing hot water in themix and keeping the mold material at about the temperature of the wateruntil it is set. In order to obtain an intimate and homogeneous mixtureof the mold material, violent agitation of the mix is necessary aspointed out in my application for molding apparatus mentioned above.

The principal object of my invention, therefore, is to obtain a mold ofthe gypsum base type which is sufficiently porous to enable the moltenmetal to flow into all the crevices of the mold cavity without beingsubjected to pressure above atmospheric, and which nevertheless willgive a relatively non-porous molding cavity surface of great smoothnessand extremely finerained.

A further important object is to make such a mold by a method employinga few simple steps and which requires a minimum of time, especiallyinthe drying or baking operation.

A more specific object is to obtain the porosity of the mold by the useof a fluid substance in the mix which may be removed later and beforethe mold is poured to leave voids uniformly honeycombing the mold body.

Still another object is to prepare such molds 45 with a minimum ofmanual handling while utilizing the smallest amount of, and leastexpensive equipment consistentwith the production of accurate, strongand well finished molds.

Other objects, and more particularly those inherent in the steps of theparticular process which I prefer, will appear as the detaileddescription of, my method progresses, it being understood that theapparatus pictured in the drawings and described is to illustrate oneway in which the several steps may be performed, and-'my process is notto be considered as limited to performance by the mechanism. Theinventive features of the process are pointed out in the appendedclaims.

Figs. 1 and 1Av together, from right to left, constitute a sideelevation view of the mold production line, and

Figs. 2 and 2A together, from right to left, constitute a plan view ofsuch line.

Fig. 3 is a cross-section of a set mold section before its removal fromthe flask and match plate, and

Fig. 4 is a perspective view of the mold section after its removal fromthe match plate and flask, being as it would appear during the drying orbaking operation.

As stated, the principal ingredient of the mold is gypsum. This issupplied commercially in the form of calcined gypsum or hemihydratehaving therein one quarter of the water capable of chemical combinationtherewith, so that it has the formula (CaSOOaHrO. This calcined gypsumwill unite chemically with water to produce gypsum represented by theformula CaSO4.2HzO

by the reaction represented by the equation given in the Toman PatentNo. 1,893,309, issued January 3, 1933. There must therefore be at leastenough water supplied to react with the calcined gypsum for settingpurposes.

In addition to the gypsum I prefer to use some I tion with the calcinedgypsum and to wet the asbestos, and then to such mixture is added enoughliquid to give the desired porosity to the finished mold. Suchliquid maybe any which can be homogeneously mixed with the water and calcinedgypsum until the latter is set, and the liquid can then beevaporatedfrom the mold to leave voids uniformly distributed through themold body. The amount of such liquid may, of.

course, also be varied within limits according to the degree of porosityof the mold desired. Sufllcient must be used to obtain the minimumdesirable porosity, and the upper limit of such liquid content is set bythe amount thereof possible to mix homogeneously with the other moldingredients, or in which the solid ingredients will remain suspendeduntil the gypsum is set. Suflicient liquid must not be used, however, toleave the mold material so porous as to be too weak to withstand thepouring stresses.

As the most satisfactory liquid I have used water greatly in excess ofthat required for chemical combination with the calcined gypsum. I havefound that a satisfactory proportion by weight of water to calcinedgypsum is two to one, whereas all that would be necessary for chemicalcombination with the calcined gypsum would be, by weight, three parts ofwater to sixteen parts of calcined gypsum, or less than one-fifth of aunit of water to one unit of calcined gypsum by weight, making theexcess water more than one and fourfifths units. For general purposes,with one hundred parts of the dry mixture having, by weight, eightypercent calcined gypsum and twenty percent (20%) asbestos pulp or fiber,may be mixed one hundred sixty parts of water, by weight, which insimple figures is four parts of calcined gypsum to one part of asbestosto eight parts of water. Less than one and one-half parts of water toone ofcalcined gypsum, by weight, will result in a mold of insufficientporosity if strengthening material is used, although proportions up toas high as three parts or more of water to one of gypsum have beenemployed where extreme porosity was desired.

The first step in the process is to mix together the dry ingredients andthen to mix these with the liquid, which, in the illustrative method tobe specifically described, is an water. While these ingredients may allbe mixed together before being placed in the flask, I prefer that thedry.

mixture and the water be placed in the flask separately and mixedtherein to allow maximum time between the mixed material being in placein the flask and the setting of the gypsum. The order in which theliquid and the dry material are supplied is not mandatory, but I preferto place the water in the flask first and thereafter to sift onto thewater surface the dry material.

In the drawings, I have shown in Figs. 1 and 2 a water supply pipe Iwhich leads from a supply.

tank (not shown) in which the water is maintained at a hot temperature,preferably about F. The valve I0 is opened until the measuring box I I,as indicated in the open-topped gauge tube I2, is full and then it isclosed. Into the shaker 2 is placed a measured amount of mixed drymaterial.

The flask and match plate unit F is slid along the table under the waterbox II and the valve I3 is turned to allow the measured amount of waterto flow from the box into the flask. Next, the flask is slid along underthe sifter 2 which is suspended flexibly and is shaken by a motormounted thereon and driving slightly eccentric weights.

When the material has all been deposited in the flask it is moved ontothe hydrator or agitator 3. To obtain an intimate and homogeneousmixture despite the great excess of liquid employed, it is necessary toagitate the mixture violently, preferably by pounding the flask supportagainst a stop so that the material will be subjected to concussion andby reason of its inertia will impinge forcibly against the flask walls.A hydrator for obtaining such action is described in detail in myapplication for molding apparatus cited above. The hydrator 3 supportsthe flask in the cradle 30 mounted on the swinging end of the arm 3|pivoted at 32. A hinged cover 33 is swung down over the flask and lockedin sealing engagement with the upper flask edge to form a closedcontainer. The motor driven shaft 34 carries an eccentric which engagesa member connected to the arm 3|, and as it rotatesit forces the flasksupport 30 downward and tensions the spring 35 which is attached to theopposite end of the arm 3|. Upon further rotation ofthe eccentric thespring pulls the flask carrying end of the arm upward so that thebifurcations 3'I impact violently against the cushioned stop 36. Themold material continues upward into impact with the cover 33 andundergoes a circulating and churning action so that every part of themixture is thoroughly and uniformly commingled.

The flask is conveyed slowly through the setthe air and all surfacescapable of transferring radiant heat surrounding the flask at a uniformtemperature, preferably at substantially the temperature of the watersupplied, namely, 180 F. If one edge of the mold material is cooled morethan the others the meniscus will be greatest, on

that edge. My 'aim is to preserve the heat content of the flask andmaterial constant, neither withdrawing heat from nor supplying heat tothem. This is accomplished by surrounding the conveyor 40 with a hood 4|and compensating for heat radiated therefrom by supplying regulated'heat beneath the hood from a heat source 42 By the time the flask hassuch as a gas flame. passed through the setting table the material hasset into the mold section M which still, of course,

contains all the excess liquid or water supplied in the mixture and isquite soft, being easily dented with the finger.

The next step is to separate the soft mold .section', as shown in Fig.3, from the flask, so that it will appear as in Fig. 4. This may be doneby an extractor such as described in my above mentioned patent, Re.21,046, or by the use of a vacuum extractor plate as therein describedmounted upon the spindle of a converted drill press 5 provided withsuitable flask holding means.

The wholly uncontained mold section is then placed on the conveyor 60 ofan oven 6 in which the excess liquid, preferably water, is dried out ofthe mold section. Moreover, substantially all the water riginally added,including that chemically combined with the gypsum, may be dried out, sothat the resulting mold is not only extremely porous but is of verylight weight. The

oven and drying method may be such as described in my application fordrying apparatus above mentioned. The mold sections are preferablyplaced on the conveyor with the parting face upward. Both the upper andlower surfaces are then subjected to direct radiant heat from heatradiating surfaces disposed above and below the mold section and spacedtherefrom about four inches. The heat of such surfaces will be within acouple of hundred degrees above or below 1400 F., which has been foundto be the most suitable average temperature for most jobs and moldcompositions.

As the vapor escapes from the mold sections it is removed from adjacentto their surfaces so that they will be blanketed as little as possiblefrom the heat radiant surfaces. For this purpose a duct system 6| may beprovided for removal of the vapor laterally from the drying chamber. Ifdesired, such removal may be expedited by the use of an exhaust blowerat the manifold exit.

The radiant surfaces may be heated principally over the entrance half bygas or oil vapor nozzles 62, the exit half being heated by withdrawingthe hot combustion gases from the combustion chambers through a hood andvent 63 at the extreme discharge end of the oven. If desired, of course,the oven may be fired over its entire length. The passage of the moldthrough the oven requires only between one and two hours ordinarily.

Upon discharge from the oven, the mold sections pass through a coolinghood I where they cool gradually instead of being subjected to thepossibility of severe stresses being set up by the sudden chilling ofmoving from the hot oven directly into the relatively cold open air. Asthe mold sections emerge from the cooling hood, the cape sections andcomplemental drag sections are ready for assembly for pouring.

The mold resulting from the described process has a substantiallyhomogeneous body of ypsum, preferably intermixed with fibrous asbestosto give additional strength. The body is honeycombed with voids whichare of minute character but very closely spaced, the solid material ofthe dried mold merely forming a skeleton. Through this structure the airand pouring gases may ooze from the mold cavity and be discharged fromthe outer mold surface. also forms an excellent insulating layer toprevent chilling of the casting metal. The mold may be made stilllighter, and the pouring gases reduced to a minimum if, in addition tothe excess water used to obtain porosity, there is dried out of the moldpart of the water chemically combined with the gypsum. In fact, I havefound that substantially all of the water added may be dried out of themold without appreciable detrimental eifects,'so that the gypsum in thefinished mold has its chemically combined water content reduced to thatof the calcined gypsum originally entering into the mixture.

The porous mold body, after the drying or baking operation, has thewater replaced by voids.

The specific gravity of calcined gypsum and asbestos is about 2.8 sothat for the previously suggested proportions in the standard mix offour parts of calcined gypsum to one part of asbestos to eight parts ofwater, by weight, the volumetric proportion of solid material to waterwould be to 8 or 1 to 4.48. Hence in the dry mold, since the compositionof the solid material is then the same as in the original mix, thevolumetric ratio of solid material or skeleton to voids is also 1 to4.48.

For the minimum water content for practical purposes mentioned, the mixis four parts of calcined gypsum to one part of asbestos to six parts ofwater, by weight, so that in the mold the volumetric proportion of solidmaterial to voids is to 6 or 1 to 3.36. If more asbestos is employedwith the same water to gypsum ratio, this ratio of solid material tovoid might occasionally be as low as 1 to 3, but greater porosity isdesirable. For cases where extreme porosity is desired, on the otherhand, such as where a mix of four parts of calcined gypsum to one partof asbestos to twelve parts of water, byweight, is used the volumetricratio of solid material to voids is Such structure seven or more timesthe volume oi solid material, for ordinary purposes the ratio will beabout four and one-half or five to one. No such proportion of void tosolidmaterial can he obtained by the use of a granular substance mixedwith the gypsum, and without the use of an excessive amount of liquidand the subsequent evaporation thereof from the mold.

Despite the high porosity or proportion of voids in the mold, themoldcavity has a surface layer which, while somewhat porous, is muchless so than the body of the mold. This layer or skin. however, is paperthin so that the air trapped in the mold cavity and the pouring gaseshave no difficulty exuding through it into the voids of the mold body.The surface, in fact, is little more porous than, and is as smooth andfinegrained as that which would be formed by the same grade of calcinedgypsum used in an article having a relatively non-porous body, namelyone formed without the use of an excessive amount of water, but withjust enough for chemical combination with the gypsum and the minimumrequired for a good mix. Since the patterns are made of metal or othernon-porous material dressed to a very smooth surface, the greatestsmoothness and fineness of surface of which the ypsum in contacttherewith is capable is obtained. I

The casting produced in the mold will in turn have a very smooth andaccurate surface, so that no finishing machine operations will berequired.

' Because of the superior insulating qualities of the porous gypsum moldand the ready escape of the air and the pouring gases, the metal willnot be chilled before entering every detail of the mold, nor will itencounter any gaseous resistance to such entry. Fine and sharp detailmay thus be obtained, and precision machine parts may be cast totolerances not exceeding plus or minus three thousandths of an inch. Ihave obtained such results both with aluminum alloys, poured at 1300 F.to 1400 F'., and with various bronze and brass alloys poured attemperatures above 2000 F. and approaching 2500 F.

As my invention I claim:

1. The method of making molds of plastic material for use as a castingmatrix, which comprises preparing an intimate, homogeneous mixture ofsolid material including calcined gypsum and asbestos, an amount; ofmixing water at least equal to that capable of combining chemically withthe calcined gypsum, and a quantity of mixing liquid, the ratio byweight of mixing water and liquid to solid material being of the orderof 1.6 to 1, and after setting of the gypsum drying out of the mold themixing liquid and substantially all the mixing water, including thatchemically combined with the gypsum,

2. The method of making molds of plastic ma-v terial for use as acasting matrix, which comprises preparing an intimate, homogeneousmixture including calcined gypsum, asbestos, and an amount of mixingwater by-weight of at least one and one fifth times the combined weightof the calcined gypsum and asbestos, allowing such mixture to set intomold form, and thereafter drying out of the mold substantially all themixing water supplied, including that part of such water chemicallycombined with the gypsum.

3. The method of making molds of plastic material, which compriseshomogeneously mixing together predetermined amounts of water andcalcined gypsum base material, allowing the resulting mixture to set anduntil set maintaining the mixture in an atmosphere having a temperatureof the order of 180 F. 4

4. The method'of making molds of plastic material, which comprisesmixing together into a homogeneous mixture water at approximately 180 F.and calcined gypsum base, solid material in the ratio, by weight, of theorder of 1.6 parts of mixing water to one part of solid material, andallowing the resulting mixture to set into mold form.

5. The method of making molds of plastic material, which compriseshomogeneously mixing together predetermined amounts of water at atemperature of approximately 180 F. and calcined gypsum base material,allowing the resulting mixture to set and until set maintaining themixture in an atmosphere having a temperature of the order of 180 F.

6. The method of making molds of plastic material, which comprisesmixing together into a homogeneous mixture water .at approximately 180F. and solid material, containing by weight a minor portion of heatresistant substance and a major portion of calcined gypsum, in theratio, by weight, of the order of 1.6 parts of mixing water to one partof solid material, allowing such mixture to set into mold section formin a flask and match plate assembly, and until set maintaining suchmixture in an atmosphere having a temperature of the order of 180 F.

7. The method of making molds of plastic material, which comprisesplacing together mixing water at a temperature of the order of 180 F.and solid material including calcined gypsum in the ratio, by weight,-ofthe order of 1.6 parts of water to one part of solid material, agitatingsuch mixture within a flask and match plate assembly and about thepatterns therein, thereby intimately depositing the mold material aboutsuch patterns, allowing such mixture to set into mold section form inthe flask and match plate assembly and until set maintaining suchmixture in an atmosphere having a temperature of the order of 180 F.,and exposing the mold to a proximate radiant heating surface at atemperature of the order of 1400 F. for approximately one hour, therebydrying out of the mold substantially all the water added to the solidmaterial in the preparation of the mixture, including that part of suchwater chemically combined with the 8. A foundry mold comprising a bodysubstantially homogeneous throughout, having therein a casting cavityfor reception of molten metal, and composed of gypsum base materialincorporating asbestos, honeycombed with voids of at least three timesthe volume of solid material, and having a smooth, relatively non-porousskin.

having a smooth skin.

HENRY F. HAGEMEYER.

